1. Field of the Invention
The present invention relates to a magnetic particle and a production method thereof as well as a magnetic recording medium containing the magnetic particle in a magnetic layer and a production method thereof.
2. Description of the Related Art
To make the size of a magnetic particle contained in a magnetic layer is required in order to increase the magnetic recording density. For example, with respect to a magnetic recording medium to be widely used in form of a videotape, a computer tape, a disk or the like, in the case the weight of a ferromagnetic substance is same, the noise decreases with decrease in particle size.
As a hopeful material for the magnetic particle to improve the magnetic recording density, CuAu type or Cu3Au type hard magnetic order alloys (e.g. refer to Japanese Patent Application Laid-Open (JP-A) No. 2003-73705) can be cited. The hard magnetic order alloys have been known to have a high crystal magnetic anisotropy due to the strains generated in an ordering process and show hard magnetism even if the size of the magnetic particle is made small.
The magnetic particle showing the hard magnetism can be produced by a liquid-phase method and a vapor-phase method and especially, a magnetic particle immediately after the production by a liquid-phase method has a disorder phase and a face-centered cubic lattice structure.
The face-centered cubic lattice thus-generated generally shows soft magnetism or paramagnetism. A magnetic particle having soft magnetism or paramagnetism is not suitable for use as a recording media. In order to obtain a hard magnetic order alloy with a coercive force of 95.5 kA/m (1,200 Oe), required for a magnetic recording medium, it required to carry out annealing at a temperature not lower than a transformation temperature at which the disorder phase is transformed to the order phase.
In the case, the foregoing magnetic particle is produced by a liquid-phase method, the metal composing a magnetic particle is required to be annealed in a non-oxidizing atmosphere of such as Ar, N2, so as not to be oxidized. However, according to the experiments performed by the inventors of the invention, when the alloy phase is ordered by annealing, occasionally, the transformation temperature is elevated. And the elevated transformation temperature causes problems in the heat resistance of a substrate, the production facilities, and the reproducibility of the magnetic characteristics.